High analysis ammonium pyrophosphate process and product



Aug. 2, 1966 T. P. HlGNETT ETAL. 3,264,085

HIGH ANALYSIS AMMONIUM PYROPHOSPHATE PROCESS AND PRODUCT Filed Feb. 1,1965 2 Sheets-Sheet 1 SUPERPHOSPHORIG ACID ANHYDROUS 74-85% P205 AMMONIA75-80% P205 (PREFERRED) 5 )8 cooum;

REACTOR I lo- /lb MOLTEN REACTED MATERIAL SOLIDIFICATION J/7 GRANULATION000mm; //3 CRUSHER 2/6 /5 FINES OVERSIZE SCREEN PRODUCT W INVENTORS.

2, 1966 T. P. HIGNETT ETAL 3,264,085

HIGH ANALYSIS AMMONIUM PYROPHOSPHATE PROCESS AND PRODUCT Filed Feb. 1.1965 2 Sheets-$heet 2 0 O 3 0 5 2 O Q 0 2 O 0 W F O 3 I 0 E m UM MO R OE 5 WE Em TT 0 O 0 O O 8 6 5 ew ES IZ 3 29520252 to HESQ PRESSURE,

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ywww United States Patent 3 264 085 HKGH ANALYSIS AMMfll llUMPYlROlPl-IUSPHATE PRUCIESS AND lPRUD UCT Travis P. l-lignett, Sheffield,and John G. Getsinger,

Florence, Ala, assignors to Tennessee Valley Authority,

a corporation of the United States Filed Feb. 1, 1965, Ser. No. 429,687

I 2 Claims. (Cl. 71-34) The invention herein described may bemanufactured and used by or for the Government for governmental purposeswithout the payment to us of any royalty therefor.

This application is a continuation-in-part of our copending applicationSerial No. 227,664, filed September 27, 1962, and now US. Patent No.3,228,752; which copending, application in turn is a division of asecond copending application Serial No. 136,960, filed September 8,1961, and now US. Patent No. 3,171,733; both of said copendingapplications filed for High-analysis Ammonium Polyphosphate Fertilizer.

Our invention relates to a new high-analysis solid fertilizer materialsuitable for preparing high-analysis liquid mixed fertilizers, and moreparticularly to a solid fertilizer material produced by reactinganhydrous ammonia and highly concentrated phosphoric acid.

Heretofore, liquid mixed fertilizers having compositions similar tothose of standard dry mixed fertilizers have been well known, and suchfertilizers are increasing in popularity in the industry. Such solutionshave numerous advantages over dry mixed fertilizers in that the costs ofevaporating moisture and bagging the product are eliminated. Such liquidfertilizers greatly simplify the operation of applying plant nutrientsto the soil.

However, liquid fertilizers have in the past had some outstandingdisadvantages. Raw-material costs have proved to be relatively high, andthe solutions produced have been so corrosive as to result in highmaintenance and storage costs. The liquid fertilizer solutions producedby the prior-art methods also have been limited to a maximum content ofplant food of about 33 weight percent. This upper limit of availableplant nutrients in prior-art solutions results from the fact thatsolutions having concentrations in excess of this amount always havebeen found to crystallize and precipitate salts out of solution whenstored at or below room temperature.

A recent breakthrough in the above-mentioned maximum content ofplant-food units in liquid mixed fertilizers is shown in US. LettersPatent 2,950,961, Marcus M. Striplin, Jr. et al., assigned to theassignee of the present invention. Striplin teaches the production ofliquid mixed fertilizers which ordinarily contain as much as 60 weightpercent plant food. Thus, unusually high percent of plant-food contentis obtained in his process by ammoniating superphosphoric acid undercontrolled conditions. Superphosphoric acid, a concentrated phosphoricacid having generally from about 72 percent to about 85 percent P 0content, is rapidly becoming a popular raw material in the fertilizerindustry for the production of liquid fertilizers.

The term superphosphoric acid used in this specification and claims isdefined as a phosphoric acid containing substantial quantities of bothorthoand polyphosphoric acids. These polyphosphoric acids includepyrophosphoric acid and other polymers from the trito the nonapolymerand higher. The proportions of po'lyphosphoric acids vary with the P 0content of the superphosphoric acid. The Canadian Journal of Chemistry,vol. 34 (1956), page 790, shows that superphosphoric acid in the rangefrom 69.81 to 84.95 percent P 0 contains the following proportions oforthophosphoric acid ice and polyphosphoric acids, expressed as percentof total phosphorus.

Alternatively, if wet-process phosphoric acid is concentrated from theusual maximum of about 54 percent P 0 up to the range of about 65 to 76percent P 0 by a process such as shown in a copending application ofJohn G. Getsinger, Serial No. 835,377, filed August 21, 1959, andassigned to the assignee of the present invention, the distribution ofortho-, pyro-, and higher polymers of the polyphosphoric acids will besomewhat dissimilar to that shown in the above-mentioned CanadianJournal of Chemistry. The presence of the impurities in suchconcentrated wet-process phosphoric acid, and the H O:P O ratio in acidso concentrated is believed to somewhat alter the distribution of thevarious polymers in this system.

The term superphosphoric acid has become widely accepted in the industryduring the past several years and it, or its analogy, polyphosphoricacid, is a generic term used to define the phosphoric acids having lesswater of constitution than orthophosphoric acid. Whereas orthophosphoricacid contains one atom of phosphorous per molecule and has a theoreticalmol ratio of water to phosphorous pentoxide of 3.0 or greater, thepolyphosphoric acids have two or more atoms of phosphorus in a chain orring structure in alternating sequence with oxygen, and a theoreticalmol ratio of water to phosphorus pentoxide less than 3. Polyphosphoricacid has two general forms, the acyclic and the cyclic, commonly calledmetaphosphoric acid. In the acyclic form, which is derived by limitedmolecular dehydration of orthophosphoric acid, the individual chains ofphosphorus and oxygen atoms have terminal ends and a theoretical molratio of water to phosphorus pentoxide between 2 and 3. Inmetaphosphoric acid, which is derived from the acyclic form by continuedmolecular dehydration, the chain is endless, forming ring structures.Metaphosphoric acids have theoretical mol ratios of water to phosphoruspentoxide of 2 or less. In practicing our invention, the acyclic speciesis formed by concentration of the ortho form; however, the concentrationor dehydration of the acid is stopped before the meta species is formed,since not only is this species ineffective in preventing the formationof precipitates in neutral salt solutions, but metaphosphoric acid formssalts with the metal impurities which are also insoluble in the acid.

The empirical formula for the desired acyclic polyphosphoric acid is:

n+2 n 3n+1 where:

H represents hydrogen. P represents phosphorus. 0 represents oxygen, andn is greater than 1.

When n=2, the species is commonly known as pyrophosphoric acid; whenn=3, the species is tripo-lyphosphoric acid.

Prior-art processes and methods for the production of concentratedfertilizers have proved to be operative; however, the industry has longfelt the need for a high-analysis solid fertilizer material which may beprocessed without the undesirable step of evaporating moisturetherefrom. In addition, the industry has desired a material which mayeither be directly applied to the soil or more preferably be readilysoluble in water for effecting the production of relativelyhigh-analysis liquid fertilizers just prior to application to the soil.The desirability of having a high-analysis solid material which isreadily soluble in water for the production of liquid fertilizers isevidenced in the prior art in efforts to dissolve diammonium phosphatein aqueous media for the production of liquid fertilizers. Liquidfertilizers so produced are limited to a maximum grade of about 8240,whereas we have found that by dissolving the product of our invention Weobtain a liquid fertilizer of grade 1l330 and higher.

Our invention is directed to a new composition of matvter which isreadily soluble in water and extremely useful as a starting material forthe production of high-analysis liquid fertilizers.

We have overcome the disadvantages inherent in both liquid mixed and drygranular fertilizers of the type shown in the prior art to a substantialextent in the present invention by providing a composition of matterwhich contains up to 80 percent of its Weight in the form of availableplant food, and which is produced by a process of directly reactinganhydrous ammonia With concentrated phosphoric acid at elevatedtemperatures and pressures. Furthermore, several new, advantageousfeatures over conventional dry mixed or liquid mixed fertilizermaterials are realized by the present invention.

Among these advantages are convenience in the preparation ofhigh-analysis liquid mixtures at or near the point of application to thesoil and the sequestration of impurities in wet-process phosphoric acid.The composition of our invention has been found to have sequestrationproperties equal to those of superphosphoric acid and the l133-0solution described in the above-mentioned Striplin et al. patent. Inaddition, the composition of our invention has advantages over theliquid mixed fertilizers mentioned above in economy and convenience oftransportation and storage. Transportation of liquid fertilizers hasbeen handicapped by lack of transportation equipment. The expense ofstoring liquid fertilizers also has prevented many manufacturers fromobtaining their supply before the peak season. During the peak season,there are not enough tank cars or trucks available to transport liquidmaterial. In addition, there exists the possibility of crystallizationof stored superphosphoric acid and liquid mixed fertilizers in extremelycold weather.

The composition of our invention is free from these disadvantages, sinceit can be shipped in readily available boxcars and stored in open binsand it is unaffected by cold weather. Finally, the material of ourinvention is extremely water soluble.

As an illustration of the above-mentioned advantageous shipping economyof the material of our invention, it has been calcullated that thefreight on 1 ton of plant food in the form of an 11-33-0 solution of thetype mentioned in the Striplin et al. patent from Sheflield, Ala., toAuburn, Wash, is about $65 However, the freight on 1 ton of plant foodbetween the same two points in the form of the composition of ourinvention is only about $35.

It is therefore an object of the present invention to provide a newsolid composition of matter and a process for its production, whichcomposition contains unusually high amounts of available plant food.

Another object of the present invention is to provide a new solidcomposition of matter and a process for its production, whichcomposition contains unusually high amounts of available plant foods andis readily soluble in Water.

Still another object of the present invention is to provide a new solidcomposition of matter and a process for its production, whichcomposition contains unusually high amounts of available plant food,which is readily soluble in water, and which may be either directlyapplied to the soil in dry form or dissolved in an aqueous medium forpreparation of high-analysis liquid fertilizers.

A further object of the present invention is to provide a new solidcomposition of matter and a process for its production, whichcomposition contains unusually high amounts of available plant food,which is readily soluble in water, which may be either directly appliedto the soil in dry form or dissolved in aqueous medium for preparationof high-analysis liquid fertilizers, and which is easily prepared fromreadily availableraw materials.

In carrying out the objects of our invention in one form thereof weemploy a reactor vessel, a stirring means, and other equipment. Ourreactor vessel and associated equipment incorporate a pressure systemwhich is operated at pressures and temperatures substantially aboveatmospheric. We have found it most economical to employ this type ofequipment for both batchand continuous-mixing operations. Our invention,together with further objects and advantages thereof, will be betterunderstood from a consideration of the following description, taken inconnection with the accompanying drawings in which:

FIGURE 1 is a flowsheet illustrating principles of our process, whichresults in a solid fertilizer having the novel properties mentionedabove.

FIGURE 2 is a graphical illustration showing the effect of reactiontemperature on the degree of ammoniation of ammonium polyphosphate.

FIGURE 3 is a graphical illustration showing the effect of pressure onthe degree of ammoniation of ammonium po lyphosphate.

Referring now more specifically to FIGURE 1, superphosphoric acid from asource not shown is fed through line 1 and any suitable means forcontrolling the rate of flow 2 into a reaction zone comprising vessel 3.Anhydrous ammonia from a source not shown is fed into vessel 3 throughline 4 and means 5 for controlling the rate of flow. Vessel 3 isequipped with a motor-driven agitator 6 running at such speed as tosecure rapid and intimate mixing of acid and anhydrous ammonia to keepthe resulting mixture in vigorous agitation until reaction is complete.Cooling coils 8 are located within vessel 3 and may be disposed in abaffle-like arrangement to increase the degree of agitation resultingfrom the action of agitator 6. We prefer to introduce a stream ofsuperphosphoric acid at a steady rate of flow according to the capacityof the equipment and to vary the rate of introduction of anhydrousammonia as may be necessary to maintain the desired pressure of excessammonia in the reactor.

The product is discharged from reactor vessel 3 through line 9 and anysuitable means for controlling the rate of flow 10 as a melt whichsolidifies upon subsequent cooling. The molten material from reactorvessel 3 is discharged into solidifier and granulator 11, where it issubjected to agitation by stirring means not shown. It has been foundthat agitation in vessel 11 is required to cause the molten material toset up into hard granules. The resulting hard granules are fed throughline 12 into cooling means 13, which may comprise a rotary cooler orother conventional cooling equipment. The cooled, hard granular materialtravels from cooling means 13 via line 14 to a screening means generallyillustrated as screens 15 and crusher 16. The crushed oversize materialand the fine material are returned to granulator 11 via lines 17 and 18,respectively.

The acid fed to reactor vessel 3 may be either electricfurnace acid orconcentrated wet-process acid. If electricfurnace acid is used, theconcentration of P 0 should be about 74 to 85 percent; however, productswith superior physical properties are made when using acid containing 75to percent P 0 Wet-process phosphoric acid can be used in this processin either batch-type or continuous-type operation. The desiredconcentration of the wet-process phosphoric acid will vary, dependingupon the impurities present therein. When wet-process phosphoric acid isused, it is preferred that the acid contain about 65 to 75 percent P Thepressure maintained in reactor vessel 3 may be in the range from aboutup to about 1000 pounds per square inch, depending upon other variablespresent in the process. However, the preferred operating pressure rangehas been determined to be about 10 to 100 p.s.i.g. Increasing thepressure increases the degree of ammoniation, and the use of pressure inreactor 3 obviates any necessity for a scrubber or other means forcontrolling loss of ammonia.

In another embodiment of our invention, the use of pressure makespossible the use of automatic control of the feed rate of the ammonia toreactor 3. This is accomplished by using an automaticpressure-regulating valve in the ammonia feed line to control thepressure in the reactor. The flow of ammonia to reactor 3 will thenautomatically be equal to the amount that can be reacted under theconditions of operation.

The temperature in reactor 3 may be maintained in the range from about325 F. to 475 R, with the preferred temperature range being about 350 F.to 385 F. Depending upon temperature and other variables, the retentiontime of the material in reactor vessel 3 may range from about 10 minutesto 3 hours, the preferred retention time being in the range of about 1to 1.5 hours. We have found that increasing the retention time increasesthe degree of ammoniation of the product.

Motor-driven agitator 6 provides vigorous agitation in reactor vessel 3and is required in order to effect intimate mixing of the anhydrousammonia with the liquid ammonium polyphosphate in reactor 3. Theintimate mixing so produced by agitator 6 has been found to increase therate of reaction in vessel 3 and therefore the degree of ammoniationwithin a given retention time.

The hard, granular product of our invention is hereinafter referred toas ammonium polyphosphate. Microscopic and chemical examinations ofproducts from varions tests using 76 percent P 0 phosphoric acid(superphosphoric acid) indicate that the product contains about 51percent to 61 percent monoammonium orthophosphate, NH H PO about 38percent to 46 percent tetraammonium pyrophosphate, (NH P O and about 2percent to 3 percent more highly condensed acyclic ammoniumpolyphosphates. The 2 to 3 percent of more "highly condensed phosphatesconsisted of a gel. Identification of such an amorphous material bymicroscopic or X-ray methods were not possible. The fact that this smallpercentage was more highly condensed than pyrophosphate was determinedby paper chromatography.

Several products made from 76 percent P 0 phosphoric acid are definedand described in Table I.

enon as the pyrophosphate has more sequestering power than the higherpolyphosphates such as tripoly-, tetrapolyphosphates, etc. This greatersequestering power means that less of the ammonium polyphosphate wouldbe needed to sequester the impurities in liquid fertilizers made withwet-process phosphoric acid, or the sequestration would be more completewith the same amount of ammonium polyphosphate.

Re-examination of data reported earlier indicates that the distributionof the phosphate species in solid ammonium polyphosphates was quitedifferent from the distribution in the superphosphoric acids used intheir manu facture. Additional tests have been made of the production ofammonium polyphosphate containing 6 pounds of ammonia per unit of P 0with acids of 76, 78, and 80 percent P 0 contents to verify and extendthe results. Conditions and results of the current tests are shown inTable II.

Ammoniation of the acids resulted in a shift of most of the triand morecondensed polyphosphates to pyrophosphate. The acids originallycontained 40 to 45 percent of their P 0 as pyrophosphate. A relativelysmall proportion of the P 0 (10% by weight) was present as triand morehighly condensed polyphosphates in acid of 76 percent P 0 content, butthe product made from this acid contained 54 percent of its P 0 aspyrophosphate. Acids of 78 and 80 percent P 0 content contained largerproportions of their P 0 as triand more condensed polyphosphates (29 and47%,. respectively); products made from these acids contained. about 80percent of their P 0 as pyrophosphates. The products were water solubleand could *be crushed and screened without difficulty.

The production of ammonium polyphosphate containing a large proportionof its P 0 as pyrophosphate may be of particular advantage because ofthe apparently superior sequestering power of pyrophosphate over morehighly condensed polyphosphates, i.e. superphosphoric acids and liquidfertilizers prepared therefrom do not contain more than 50 percent oftheir P 0 as pyrophosphate.

In a preliminary test with a still more highly condensed superphosphoricacid (83 percent P 0 acid) the product had a low degree of ammoniation(4.9 lb. NH /unit of P 0 The change in distribution of the phosphateswas different than in the tests with less concentrated acids. Asubstantial portion of the trito nonapolyphosphates was converted tospecies more condensed than nonapolyphosphates (Table II). Thus, itappears that the observed shift to a material containing unusually highamounts of the pyrophosphate species occurs only when thesuperphosphoric acid used contains a P 0 concentration in the somewhatnarrow range of about 78 percent TABLE I.DESORIPTION OF AMMONIUMPOLYPHOSPHATE PRODUCT MADE FROM 76 PERCENT P 0 II-IOSPHORIO ACID Whenacid with P 0 concentration of 78 to 80 percent was used, productcontaining 86 to 88 percent ammonium pyrophosphate was made. Theremainder of the product was ammonium orthophosphate. The pyrophosphatecontent was surprisingly high and indicated that a shift towardpyrophosphate took place during the ammoniation of the acid. This is afortunate and useful phenomto percent by weight, whereas superphosphoricacids utilized which are either more highly condensed or less condensed,i.e. contain greater than 80 percent P 0 or less than 78 percent P 0 donot when ammoniated, according to our teachings, exhibit this shift ofthe various species toward the pyrophosphate member.

In addition, we have found that when we prepare ammonium polyphosphatesthrough the use of super acid containing in the range of 78 percent to80 percent P the resulting material which displays this unexpected shifttoward the high pyrophosphate content is an excellent intermediatecomposition for a simple and direct production of reagent grade ammoniumpyrophosphate. We have found that the solid material from our processwhich is made from acid originally containing in the range of 78 percentto 80 percent P 0 may be so utilized in the production of reagent gradeammonium pyrophosphate in the following manner. The material may bemixed with a minimum amount of water to produce a relatively thickSIIUITY. The slurry is then subsequently slowly ammoniated so as toproduce large and easily filterable crystals of triammoniumpyrophosphate monohydrate. Following this procedure we have found thatat least 70 percent of the phosphate can be recovered as a reagent gradeammonium pyrophosphate. If desirable, the solution phase which is leftmay be either directly used as a fertilizer or may be returned asrecycle to the production of ammonium polyphosphate. This procedure forproducing reagent grade ammonium pyrophosphate, due to its relativesimplicity, is at the present time the most desirable method of which weare aware. Other methods of the prior art, although useful, are, for themost part, quite tedious for producing a desired reagent grade. One ofsuch prior art methods is that shown in a copending application of JamesR. Lehr, Serial No. 361,624, filed April 20, 1964, which process isconcerned with the production of ammonium pyrophosphate by themetathetical reaction between fluoride and various calciumpyrophosphates or calcium acid pyrophosphate compounds.

sures of up to about 325 p.s.i.g. as required. The ammonia was fed intothe reactor through a %-inch tube. The tube was closed at the end, and aone-hole sparger was made by drilling a 0.052-inch hole at the end ofthe tube. The sparger was located near the bottom of the reactor underthe tip of the agitator. The reactor was equipped with a pressure gage,and the rate of feed of ammonia to the reactor was controlled manuallywith a throttling valve to give the desired pressure of excess ammoniain the reactor. The temperature was measured with a thermocouple and arecording potentiometer.

Since the reaction of ammonia and superphosphoric acid was highlyexothermic, it was necessary to provide cooling. Hot water was used forcooling to prevent freezing of material on the cooling coil (freezingpoint of about 325 F.). The cooling coil was made of /a-inch stainlesssteel (A.I.S.I. Type 316) tubing. It provided 1 square foot of coolingarea based on the external surface of the coil. The water was pumpedthrough the cooling coil and discharged into a 1.5-gallon tank, fromwhich it was recycled. This arrangement provided for utilizing the heatof reaction to heat the makeup water. The supply of cooling water in thetank remained at 212 F. Water was added to the supply tank as requiredto replace that evaporated.

Two electrical conductivity probes (electrodes), entering from the topof the reactor, were used to measure the level of the liquid in thereactor. The tips of the probes were /2 inch apart vertically. Eachprobe and the shell of the reactor formed a conductivity circuit. Theliquid in the reactor completed the circuit when it touched a probe andcaused a light bulb to burn. The reactor was TABLE II.PRODUCTION OFAMMONIUM POLYPI-IOSPHATE: CHAN GE IN DISTRIBUTION OF PHOSPHATE SPECIESON AMMONIATION SUPERPHOSPHORIC ACID Total P 0 percent by wt Distributionof phosphate species in acid,

percent of total P205 as:

Orthophosphate Pyrophosphate Trito nonapolyphosphate Higher thannonapolyphosphate HbkK omes REACTION CONDITIONS Continuous Type ofoperation Acid feed temperature, F Ammoniation temperature, 1LAmmoniation pressure, p.s.i.g Retention time, min

AMMONIUM POLYIIIOSPHATE Distribution of phosphate species, percent oftotal P 0 as:

Orthophosphate Pyrophosphate Trito nonapo1yphosphate Higher thannonapolyphosphate Chemical analysis, percent by wt.:

Total N Total P205 POllXldS NIIg/llflit P205 Water-soluble P205, percentof total P205 a Distribution of phosphate in 78.1 percent P205 acidobtained by chromatographic analysis; distribution in other acidsobtained from Can. J. Chem. 34, 785-97 (1956).

b Maximum values.

The reactor for producing the ammonium polyphosphate was constructed ofstainless steel (A.I.S.I. Type 316) and was of l-gallon capacity. It wasequipped with a turbine-type agitator and four baffles /2 inch in widthby 11 inches high. Acid was fed from an overhead tank (25-galloncapacity) with a reciprocating piston-type pump. The length of stroke ofthe piston could be varied to give the desired feed rate. The acid wasfed at rates to give 10 to 30 pounds of product per hour.

Gaseous ammonia was fed through a /2-inch line from pressure cylinderslocated outside the laboratory building.

operated to keep the level between the two probes, which was indicatedby the top light being off and the other on. The level was controlled bythe rate of drawoif of liquid from the bottom of the reactor by use of aA-inch throttling valve.

In the initial tests it was found that the degree of agitation in thereactor had a significant eifect on the degree of ammoniation. Thereactor first was equipped with a sixblade agitator impeller that was 2%inches in diameter with blades /2 inch in width located one agitatordiameter above the bottom of the reactor. The agitator was ro- Warmwater was sprayed on the cylinders to obtain prestated at 600 r.p.m.,and the degree of ammoniation was only about 5 pounds of ammonia perunit of P Increasing the width of the agitator blades to 2 inchesincreased the degree of ammoniation to 6.3 pounds of ammonia per unit ofP 0 when the speed of the agitator was 600 r.p.m. A further increase indegree of ammoniation to 7.5 pounds of ammonia per unit of P 0 resultedwhen the speed of the agitator was increased to 1730 r.p.m. No furtherincrease was obtained when the speed of the agitator was increased to2130 r.p.m. Effects of operating variables on the degree of ammoniationin tests of the production of ammonium polyphosphates are given in TableIII.

TABLE III.EFFECTS OF OPERATING VARIABLES Product com- Speed of agitator,Tempera- Pressure, Retention position Lb NIFIs/ r.p.m. ture, F. p.s.i.g.time, unit P 05 minutes EFFECT or PRESSURE EFFECT or TEMPERATURE EFFECTor RETENTION TIME 2 Agitator, 2.5 inches in diameter and inch wide.

Temperature and pressure were related in their effects on the degree ofammoniation and on the freezing point of the melt in the reactor. Atpressures of 300 p.s.i.g., it was necessary to keep the temperature at415 F. so that the melt would be fluid; at pressures of 25 p.s.i.g,temperatures as low as 365 F. could be used. The tests were made with anagitator speed of 2130 r.p.m. and a retention time of about 60 minutes.The results are shown in Table III and FIGURES 2 and 3.

The effect of pressure was measured at a reaction temperature of415" F.Increasing the pressure from 25 to 300 p.s.i.g. increased the degree ofammoniation from 5.7 to 7.5 pounds of ammonia per unit of P 0 Tests ofthe effect of temperature were made at a pressure of 25 p.s.i.g.Increasing the temperature from 365 F. to 450 F. decreased the degree ofammoniation from 7.0 to 5.3 pounds of ammonia per unit of P 0 At areactor pressure of 25 p.s.i.g. and temperatures of 350 F. to 370 F., asthe retention time was increased from 30 to 90 minutes, the degree ofammoniation increased from 6.8 to 7.2 pounds of ammonia per unit of P 0It is apparent that there are several combinations of Example ISuperphosphoric acid (76% P 0 was fed to the reactor at the rate of 2.6pounds per hour. The flow of ammonia was regulated to give a pressure of300 p.s.i.g. in the reactor. This resulted in a flow rate of 0.7 poundof ammonia per hour. The volume of the liquid retained in the reactorwas 0.7 gallon. The retention time of the liquid in the reactor was 168minutes. The temperature in the reactor (380 F.) was controlled byregulating the flow of Water through the cooling coil. The agitator (2%in., six-blade impeller) was rotated at 1000 r.p.m. Liquid product wasdischarged from the reactor at the rate of 3.3 pounds per hour. Aftercollecting 9 pounds of liquid product, it was agitated with apropellertype stirrer for 15 minutes until it solidified. The solidmaterial was crushed and sampled for analysis. The analysis showed anitrogen content of 17.9 percent and a P 0 content of 60.8 percent. Theproduct was hard. It remained dry and free flowing even after exposureto a humid atmosphere.

Example 11 In a run made in a reactor device similar to that describedin Example I, the following results were obtained.

TEST NO. 1

Superphosphoric acid concentration, percent P 75.9 Feed rate, lb./hr.:

Superphosphoric acid 25.0 Anhydrous ammonia 6.1 Reactor:

Agitator speed, r.p.m. 1000 Temperature, F. 420 Pressure, p.s.i.g. 300Retention time, minutes 18 Discharge rate, lb./ hr 31.1

Product grade 15.9-61.0-0

The analysis of the above product indicates a fertilizer material ofabout 16-61-0 grade, and the material produced in this run remained dryand free flowing even after exposure to a humid temperature.

Example 111 The results of another run made in a reactor device similarto that described in Example I are given below.

TEST NO. 2

Superphosphoric acid concentration, percent P 0 76.1 Feed rate, lb./hr.:

Superphosphoric acid 3.8 Anhydrous ammonia u 0.9 Reactor:

Agitator speed, r.p.m. 1000 Temperature, F. 340 Pressure, p.s.i.gRetention time, minutes 118 Discharge rate, lb./ hr 4.7

Product grade 16.662.50

The analysis of the above product indicates a fertilizer material ofabout 17-63-0 grade, and the material produced in this run remained dryand free flowing even after exposure to a humid atmosphere.

Example IV In still another run made in a reactor similar to thatdescribed in Example I, the following results were obtained.

TEST NO. 3

Superphosphoric acid concentration, percent P 0 75.7

The analysis of the material made in this run indicated a fertilizermaterial of grade of about 620, and the material so produced remaineddry and free flowing even after exposure to a humid atmosphere.

Example V The following results were obtained in another run made in areactor device similar to that described in Example 1.

TEST NO. 4

Superphosphoric acid concentration, percent P 0 76.4 Feed rate, lb./hr.:

Product grade ..V 17.8-59.7-0

12 The analysis of the material made in this run indicated a fertilizermaterial of a grade of about 18-60-0, and the material so producedremained dry and free flowing even after exposure to a humid atmosphere.

Example VI The results of yet another run are given below. The reactorin which this run was made was a device similar to that described inExample I.

TEST N0. 5

Superphosphoric acid concentration, percent P 0 76.3 Feed rate, lb./hr.:

Superphosphoric acid 6.9 Anhydrous ammonia 1.9 Reactor:

Agitator speed, r.p.m. 2130 Temperature, F. 365 Pressure, p.s.i.g 25Retention time, minutes 60 Discharge rate, lb./ hr 8.8

Product grade 17.3-59.8-0

The product material analyzed about 17600, and it remained dry and freeflowing even after exposure to a humid atmosphere.

Example VII The following results were obtained in yet another run madein a reactor device similar to that described in Example I.

TEST N0. 6

Superphosphoric acid concentration, percent P 0 76.1 Feed rate, lb./hr.:

slurry was sprayed through a nozzle directly onto a bed of recycledfines in a laboratory-size pugmill. Recycled fines (-12 mesh, Tyler)were fed to the pugmill by a disk feeder. The recycle rate was poundsper hour or 3.3 pounds per pound of product. The temperature of thematerial discharged from the pugmill was F. The screen analysis (Tyler)of the material from the pugmill was as follows:

Percent i M :2 23.1 16.8 24.6 35.5

The product was hard, dry, and free flowing even after exposure to ahumid atmosphere.

Example VIII Wet-process phosphoric acid which had been highlyconcentrated (71.4% P 0 was reacted batchwise with gaseous ammonia in apressure-type reactor equipped with a propeller-type agitator. Theprocedure used is given below.

The acid (200 g.) was added to the reactor, and the reactor was closed.The reactor was then heated to 200 F. Gaseous ammonia (45 g.) was addedat an average rate of 1.3 grams per minute for 35 minutes. At this timethe reactor temperature had risen to a maximum of 325 F., and thepressure was 65 pounds p.s.i.g. Feeding of ammonia and agitation werediscontinued at this time, the pressure was released, and the fluidmixture was poured out of the reactor. A longer period of reaction andagitation would have resulted in solidification of the 13 material inthe reactor. The fluid material from the reactor was agitated by handstirring until the material became hard. Analysis of the product gave anitrogen content of 15.2 percent and a P content of 58.4 percent. Thematerial was hard and free flowing.

While we have shown and described particular embodiments of ourinvention, modifications and variations thereof will occur to thoseskilled in the art. We wish it to be understood, therefore, that theappended claims are intended to cover such modifications and variationswhich are within the true scope and spirit of our invention.

What we claim as new and desire to secure by letters patent of theUnited States is:

1. A process for the production of reagent grade ammonium pyrophosphatefrom anhydrous ammonia and highly concentrated phosphoric acid, whichprocess com- ,prises the steps of maintaining in a closed reactionvessel at a temperature in the range from about 300 F. to about 500 F.and under a constant positive pressure in the range from about p.s.i.g.to about 1000 p.s.i.g. a mass of molten material of low viscositypreviously formed by combining in said closed reaction vessel saidanhydrous ammonia with said highly concentrated phosphoric acid, saidhighly concentrated phosphoric acid containing in the range from about78 percent by weight P 0 to about 80 percent by weight P 0 continuouslycombining relatively small streams of said anhydrous ammonia and saidhighly concentrated phosphoric acid into said mass; continuouslyvigorously agitating said mass thereby keeping substantially the entiremass well agitated and effecting immediate ammoniation of said inflowingacid; withdrawing from the bottom of said mass surplus molten ammoniumphosphate material; combining said withdrawn ammonium polyphosphatematerial with aqueous medium to form a slurry therewith; subsequentlyadjusting the pH of said slurry by the iamrnoniation thereof to a finalpH in the range from 5 .0 to 6.3 there-by effecting a recrystallizationof the diammonium pyrophosphate phase to the triammonium pyrophosphatemonohydrate in the form of easily filtrable crystals thereof; andseparating said crystals of triammonium pyrophosphate monohydrate asproduct.

2. A new composition of matter containing a total plant food content(N+P O in the range from about 78 percent to about 80 percent by weightand consisting essentially of a solid mixture of solid water-solublesalts containing about 14 per-cent to about 16 percent monoammoniumorthophosphate, NH H PO from about 76 percent to about 84 percentammonium pyrophosphate, (NH4)X(H4 X)P20']; and from about 2 percent to 8percent of the more highly condensed acyclic ammonium polyphosphates inthe group comprising ammonium tripolyphosphate through ammoniumnonapolyphosphate.

References Cited by the Examiner UNITED STATES PATENTS 1,699,093 1/1929Carothers 23-106 2,105,446 1/1938 Wilson 23106 2,288,418 6/1942Partridge 23-106 2,592,273 4/1952 Goebel 23-106 2,856,279 10/1958Hignett 23106 3,005,696 lO/196l Hignett 7164 DONALL H. SYLVESTER,Primary Examiner.

T. D. KILEY, Assistant Examiner.

1. A PROCESS FOR THE PRODUCTION OF REAGENT GRADE AMMONIUM PYROPHOSPHATEFROM ANHYDROUS AMMONIA AND HIGHLY CONCENTRATED PHOSPHORIC ACID, WHICHPROCESS COMPRISES THE STEPS OF MAINTAINING IN A CLOSED REACTION VESSELAT A TEMPERATURE IN THE RANGE FROM ABOUT 300*F. TO ABOUT 500*F. ANDUNDER A CONSTANT POSITIVE PRESSURE IN THE RANGE FROM ABOUT 10 P.S.I.G.TO ABOUT 1000 P.S.I.G. A MASS OF MOLEN MATERIAL OF LOW VISCOSITYPREVIOUSLY FORMED BY COMBINING IN SAID CLOSED REACTION VESSEL SAIDANHYDROUS AMMONNIA WITH SAID HIGHLY CONCENTRATED PHOSPHORIC ACID, SAIDHIGHLY CONCENTRATED PHOSPHORIC ACID CONTAINING IN THE RANGE FROM ABOUT78 PERCENT BY WEIGHT P2O5 TO ABOUT 80 PERCENT BY WEIGHT P2O5;CONTINUOUSLY COMBINING RELATIVELY SMALL STREAMS OF SAID ANHYDROUSAMMONIA AND SAID HIGHLY CONCENTRATED PHOSPHORIC ACID INTO SAID MASS;CONTINUOUSLY VIGOROUSLY AGITATING SAID MASS THEREBY KEEPINGSUBSTANTIALLY THE ENTIRE MASS WELL AGITATED AND EFFECTING IMMEDIATEAMMONIATION OF SAID INFLOWING ACID; WITHDRAWING FROM THE BOTTOM OF SAIDMASS SURPLUS MOLTEN AMMONIUM PHOSPHATE MATERIAL; COMBINING SAIDWITHDRAWN AMMONIUM POLYPHOSPHATE MATERIAL WITH AQUEOUS MEDIUM TO FORM ASLURRY THEREWITH; SUBSEQUENTLY ADJUSTING THE PH OF SAID SLURRY BY THEAMMONIATION THEREOF TO A FINAL PH IN THE RANGE FROM 5.0 TO 6.3 THEREBYEFFECTING A RECRYSTALLIZATION OF THE DIAMMONIUM PYROPHOSPHATE PHATEPHASE TO THE TRIAMMONIUM PYROPHOSPHATE MONOHYDRATE IN THE FORM OF EASILYFILTRABLE CRYSTALS THEREOF; AND SEPARATING SAID CRYSTALS OF TRIAMMONIUMPYROPHOSPHATE MONOHYDRATE AS PRODUCT.
 2. A NEW COMPOSTION OF MATTERCONTAINING A TOTAL PLANT FOOD CONTENT (N+P2O5) IN THE RANGE FROM ABOUT78 PERCENT TO ABOUT 80 PERCENT BY WEIGHT CONSISTING ESSENTIALLY OF ASOLID MIXTURE OF SOLID WATER-SOLUBLE SALTS CONTAINING ABOUT 14 PERCENTTO ABOUT 16 PERCENT MONOAMMONIUM ORTHOPHOSPHATE, NH4H2PO4; FROM ABOUT 76PERCENT TO ABOUT 84 PERCENT AMMONIUM PYROPHOSPHATE, (NH4)X(H4-X)P2O7;AND FROM ABOUT 2 PERCENT TO 8 PERCENT OF THE MORE HIGHLY CONDENSEDACYCLIC AMMONIUM POLYPHOSPHATES IN THE GROUP COMPRISING AMMONIUMTRIPOLYPHOSPHATE THROUGH AMMONIUM NONAPOLYPHOSPHATE.